BACKGROUND. Actin is largely responsible for cell motility and is only sparsely found in normal epithelial cells. An altered expression of actin in some malignancies may facilitate aggressive invasion. Micronodular basal cell carcinoma (BCC) has been shown to require more surgical stages, wider tissue margins, and deeper defects for extirpation during Mohs micrographic surgery relative to nodular BCC. OBJECTIVE. To provide preliminary data regarding a possible correlation between alpha-smooth muscle actin (α-SMA) expression within the cells or stroma of micronodular BCC and aggressive invasion. In addition, the incidence of α-SMA expression in micronodular, morpheaform, and nodular BCC is evaluated. METHODS. Nine micronodular basal cell carcinomas (7 primary, 2 recurrent) were evaluated for neural invasion, depth of tissue invasion, and alpha smooth muscle actin antibodies. The presence of alpha-smooth muscle actin antibodies was assessed using immunoperoxidase staining and compared with 13 morpheaform (13 primary, 0 recurrent) and 12 nodular (12 primary, 0 recurrent). RESULTS. Six of the nine micronodular (67%), eight of the 13 morpheaform (62%), and 0 of the 12 nodular (0%) BCCs stained positive for α-SMA. Of the six micronodular BCCs that stained positive for α-SMA, three invaded the fascia or muscle and three displayed neural invasion. In contrast, of the three micronodular BCCs that stained negative for α-SMA, none invaded the fascia or muscle and only one exhibited neural invasion. CONCLUSION. Actin was present in 66% of micronodular, 62% of morpheaform, and 0% of nodular BCC. The presence of actin in micronodular BCC may be a marker for aggressive invasion.
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